With a prior art power module of the type that is cooled on both sides, electrical wiring, an insulation layer, and a cooling device are provided on one principal surface upon which electrodes of internal power semiconductor elements are formed, and also electrical wiring, an insulation layer, and a cooling device are provided, in a similar manner, on its other principal surface as well. A heat dissipation base and fins are formed on the side opposite to the side where the power semiconductor devices are placed, which, moreover, are dipped into the water passage housing internal to the cooling device described above, in which a cooling water passage is formed by sealing with resin material, through which the fins become in direct contact with the cooling medium and thus the heat generated by the power semiconductor device is dissipated from both principal surfaces via the cooling device. The structure like this for enhancing the cooling performance and the productivity is disclosed in Patent Documents #1 through #3.
In Patent Document #1, a power module is described of a type that is cooled on only one side and with which heat is dissipated from one principal side thereof, including electrical wiring, an insulation layer, and a cooling device on one principal surface of power semiconductors, and in which a cooling device is adhered to the electrical wiring with an insulating adhesive and an inorganic insulation layer is formed at the interface between the insulating adhesive and the cooling device, so that the insulation performance is enhanced by this double layer insulation material consisting of the insulating adhesive and the inorganic insulation layer.
With a prior art power conversion device, since heat is generated by the power semiconductors that are provided at the upper side of the cooling device for the power module, accordingly a construction is required in which a heat dissipation base and fin portions are provided to the cooling device, and the cooling medium flows directly over the fin portions so as to cool them. However, with electric vehicles and so on that are becoming widespread, there is a requirement for yet further increase of output and for yet further reductions in size of the power conversion device. It is necessary to enhance the cooling performance in order to implement increase of output and reduction in size, and for this it is necessary use power semiconductors that are large in order to increase the areas of their cooling surfaces, and thus to lower the thermal resistance. While, by increasing the size of the power semiconductors, it is possible to reduce the thermal resistance with respect to the cooling medium by increasing the heat dissipation area, on the other hand the size of the power conversion device increases along with increase in size of the power semiconductors, and at the same time the productivity is also deteriorated. As a means for enhancing the productivity, there is an expedient of omitting a brazing process by changing the insulation material from the ceramic that is used in the prior art to an adhesive insulating resin material. However, the insulation performance of the resin insulation material itself is inferior as compared to a ceramic, and, since permeation of the cooling medium or moisture from outside exerts a negative influence upon the performance for adhesion to the cooling device and upon the insulating performance, accordingly there is a problem in the field of application to in-vehicle devices, for which high reliability is demanded.
The constructions disclosed in Patent Documents #1 through #3 are constructions in which various insulation layers are interposed between the electrical wiring and the cooling device using an organic type insulation material, of which resin material is representative, and there is the problem of deterioration of the insulation due to mechanical stress and other complex types of stress along with changes in the temperature of the environment of use.
With the construction disclosed in Patent Document #4, there is the problem that heat dissipation is performed from only one surface of the power semiconductors, so that the cooling performance is low. Moreover, no sealing between the internal electronic components and the cooling medium is described. If the cooling medium should seep in, then the adhesive strength of the insulating adhesive and the insulation performance between the insulating adhesive and the inorganic insulation layer itself will deteriorate, and as a result it will become impossible to maintain the insulation performance of the insulating substrate. This is a problem in the field of equipment for vehicles, for which high reliability is demanded. In particular, it is very important for organic materials such as insulating adhesives, of which resin is representative.